Un-partitioned hvac module control for multi-zone and high performance operation

ABSTRACT

A method controls the discharge of temperature-conditioned air from a plurality of zone outlets of an automotive HVAC system via an open architecture multi-zone HVAC unit having a single blower fan, an evaporator downstream of the blower and a heater downstream of the evaporator, wherein each zone in the module includes a temperature mix door for proportioning hot and cold air, which is controlled by a separate Discharge Temperature Maintenance control (DTM control), and an output valve for controlling a zonal output flow rate. The output valve of each zone outlet is placed in an output valve position associated with a target resistance; and the single blower fan is operated at a minimum voltage required for generating a total requested blower output flowrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-in-Part of U.S. application Ser. No. 14/282,173, filed on May 20, 2014, and entitled “UN-PARTITIONED HVAC MODULE CONTROL FOR MULTI-ZONE AND HIGH PERFORMANCE OPERATION” the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD OF INVENTION

The present invention relates to an HVAC system and method for the discharge of temperature-conditioned air from a plurality of zone outlets of an automotive HVAC system in an energy-efficient manner.

BACKGROUND OF THE INVENTION

In an automotive vehicle, limited space is allotted beneath or in front of the instrument panel for the heating, ventilation, and air conditioning (HVAC) system. In vehicles having a single zone system compactly designed to fit within the allotted space, it is sometimes desirable to provide an additional temperature-controlled zone. A system with multiple temperature-controlled zones allows the driver and passenger to have separate controls of the temperature in their respective zone thereby maximizing the comfort of each individual. Extending the zone system even further, i.e., a separate control for the rear seat region, may also be desirable.

Single zone systems are generally designed to optimally utilize the amount of available space in a given type of vehicle as well as to conform to the shape of that space. When a dual zone system is designed, it generally must conform to the same size and shape, thereby requiring additional functions to be added without utilizing any extra space. Moreover, when a dual zone system is provided for a particular vehicle line, it is often desired to offer to customers the option of a less expensive single zone system as well. However, the designing and tooling of different systems is sometimes prohibitive for some vehicle models.

HVAC modules produced for use in vehicles typically provide temperature control either to a single zone or to dual zones, i.e., the entire HVAC module is dedicated to one or the other. HVAC modules that have the capability of providing temperature control for an additional zone are specifically designed, tooled and manufactured for the exact number of zones. The production volume (or number of vehicles) for multiple zone modules is typically much lower than that for single or dual zone modules. As such, it is much more expensive to design such a multiple zone module for so few vehicles. Additionally, it would be disruptive to the manufacturing cell and the manufacturing process in general to be forced to build an entirely different HVAC module to achieve an additional temperature-controlled zone.

The HVAC units of the prior art provide for multiple, separate streams of temperature-conditioned air being fed to multiple zones. U.S. Pat. No. 6,772,833 B2 to Auer, et al. provides for an HVAC unit including an evaporator, a heater core, a blower, a plurality of blending chambers and an insert mounted within the housing. The insert controls the flow of conditioned air from the blending chambers thus providing multiple separate streams of temperature-conditioned air to multiple zones.

U.S. Pat. Nos. 6,772,833 B2 and 7,832,464 B2 are hereby incorporated herein in their entirety.

Although the prior art provides for an HVAC unit capable of producing multiple temperature-controlled streams of air to be fed to multiple vehicle zones, a different HVAC unit must be designed and tooled for each discrete number of temperature-controlled streams, i.e., an entirely different HVAC unit for each number of independently temperature-controlled streams for different zones.

Traditional heating, ventilation and air conditioning (HVAC) modules use partition walls extending up to the evaporator in the HVAC module to provide multiple streams of conditioned airflow. These multiple streams of airflow are used to achieve multi-zone climate control in the associated vehicle passenger compartment. Dual-zone or tri-zone climate control systems based upon this type of HVAC module are frequently employed in modern passenger vehicles. Due to operating capacity and packaging constraints, two separate and partitioned HVAC modules are occasionally employed in large vehicles, such as sport utility vehicles (SUV) and mini-vans, to achieve multi-zone operation, where one module is installed in the area of the vehicle dash and another in the area of the trunk.

However, implementation of the traditional, partitioned, dual HVAC module approach is problematic. For example, they can require excessive packaging space in the host vehicle, more air ducts, more lines and fittings, more refrigerant (typically about 2 extra lbs.), more coolant, more mass, higher operating noise levels, higher cost and increased system complexity that often translates into elevated quality and warranty issues. Such systems require more energy and larger supporting components such as compressors, water pump, condenser, alternator, line sets and ducts. As a consequence, the dual module approach results in increased vehicle fuel consumption and increased exhaust emissions. All of these items significantly contribute to overall vehicle cost and operating costs.

BRIEF DESCRIPTION OF THE INVENTION

The present invention pertains to the control of a high performance HVAC module with enough capacity to replace dual modules presently employed within large vehicle climate control systems. In particular, the present invention provides a control for such HVAC systems, in which positions of mix doors that set cross-sections of hot and cold air stream paths to zone outlets are controlled by a Discharge Temperature Maintenance (DTM) control that is external to the HVAC module airflow control. The DTM control may be part of an Automatic Climate Control system embedded controller unit that interacts with and commands over the HVAC airflow controller unit, or it may be a code block belonging to the Automatic Climate Control system that interacts with and commands over the HVAC airflow control block within the same embedded controller. In both cases the HVAC airflow control loses the capability to position the mix doors, but is still required to respond to the mix door position changes to maintain the zonal airflow. In such HVAC systems, the HVAC control directly responds to zonal commands for airflow from the Automatic Climate Control system and attempts to maintain the zonal airflows by adjusting the blower output via the blower voltage and the zonal air streams by positioning zonal output valves. As the DTM control may adjust zonal mix door positions in response to Automatic Climate Control, the HVAC airflow control in turn reacts to such changes by readjusting the blower and output valve settings until a convergence of targeted zonal temperatures and zonal air streams with actual zonal temperatures and zonal air streams is achieved.

In a multi-zone HVAC system, different zone outlets may have different structures or mechanisms for regulating the output of air at each zone outlet. The zone outlets in the front may have mode valves functioning as flow control valves, while the zone outlets in the rear of the vehicle may have dedicated flow control valves. In the following description, regardless of the type of valves or mechanisms used for controlling the output at each zone, all of these mechanisms are, without limitation, called “output valves.”

While running the fan of the high performance HVAC unit at maximum power will supply all zone outlets with sufficient air flow for any operator-requested settings, such HVAC control would consume an undesirably high amount of energy. The present invention provides a method to supply multiple zones with differing airflow requests at a minimal possible blower voltage for a system with a separate Discharge Temperature Maintenance control

For example, the method includes the steps of reading an operator-, or Climate-Control-System-requested zonal discharge blower rate for each of the zone outlets; converting each zonal discharge blower request to a zonal flowrate request; determining a pressure drop associated with each mix door position dictated by the DTM control; determining, for each zone outlet, a target resistance for each output valve based on the zonal flowrate request and on the pressure drop associated with the mix door position; placing the output valve of each zone outlet in an output valve position associated with the target resistance; and operating the single blower fan at a minimum voltage required for generating the total output flowrate request.

The method is further optimized by the steps of setting an initial blower operating voltage; determining a minimum resistance for at least one of the output valves based on a comparison of the target resistances of all zone outlet; determining for each of the output valves a respective individual normalized resistance deviation of the calculated individual output valve resistance from the individual minimum attainable output valve resistance; placing the each output valve in an adjusted output valve position associated with the respective individual normalized resistance deviation; and modifying the blower voltage to operate the single blower fan at a minimum voltage required for generating the total output flowrate request with the at least one of the output valves set to the minimum resistance.

The method may include the step of determining the adjusted output valve position for each zone based on an average pressure downstream of each mix door, the average pressure being a combination of a hot air pressure and a cold air pressure downstream of each mix door. This simplifies the calculations because only one pressure value per mix door needs to be considered.

The method is further refined by the step of determining an individual normalized resistance deviation of the calculated individual output valve resistance from the individual minimum attainable output valve resistance for each of the output valves; wherein the step of adjusting the blower voltage brings at least one of the individual normalized resistance deviations below a predetermined threshold ratio.

The minimum attainable resistance of each output valve may be based on predetermined stored output valve calibration data.

The threshold ratio for the individual normalized resistance deviations preferably amounts to at most about 5%.

Initially, each output valve may be set to a fully open position with minimal flow resistance until each output valve is placed in an output valve position associated with the respective individual normalized resistance deviation.

The method may be simplified by calculating an average zonal mixing pressure in a mixing chamber between each one of the mix doors and an associated output valve. The average mixing pressure can be chosen as a value between a hot air pressure and a cold air pressure passing the mix door. From the average mixing pressure of each zone a desired output valve resistance can be calculated based on the desired zonal flowrate.

Further details and benefits of the present invention will become apparent from the following description of examples of preferred embodiments illustrated in various drawings. The drawings are provided purely for illustrative purposes and are not intended to limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1, illustrates a perspective view of a high performance HVAC module with enough capacity to replace dual modules presently employed within large vehicle climate control systems;

FIG. 2, illustrates a cross-sectional view of the high performance HVAC module of FIG. 1 which is modified to include separate front mode and rear mode cases, depicting internal details thereof;

FIG. 3, illustrates a HVAC control circuit employing flow rate sensing;

FIG. 4 is a flow chart illustrating the implementation of a zonal airflow balance algorithm of the system defined in FIG. 3;

FIGS. 5 and 6, illustrate a HVAC control circuit with an embedded controller providing airflow balance with a HVAC math model;

FIG. 7, is a flow chart illustrating the implementation of a modified control algorithm with a HVAC module math mode defined in FIGS. 5 and 6;

FIG. 8, illustrates a HVAC module math model calibration sensor employing, by way of example, a single air velocity sensor installed before the evaporator and after the blower;

FIG. 9, is a flow chart illustrating the implementation of a velocity sensor management algorithm wherein a non-limiting number of ignition cycles is used to initiate the reading of the sensor in the field;

FIG. 10, is a flow chart illustrating the implementation of a HVAC module correction algorithm wherein the variables “V_newcar” and “V_current” are read before the HVAC module mathematic model is run to estimate the model zonal flow rates Qi;

FIG. 11, is a flow chart illustrating the control steps to be taken to achieve “Super Mode” operation;

FIG. 12 is a flow chart illustrating and example of the operation of a centrally controlled Discharge Temperature Measurement system (DTM system);

FIG. 13 is a flowchart showing the general method steps of an HVAC control operating along a DTM system; and

FIGS. 14A and 14B in combination form a flow chart showing a more detailed subroutine for adjusting output valve positions in the HVAC system.

Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF INVENTION

Referring to FIG. 1, the present invention pertains to a high performance HVAC module with enough capacity to replace dual modules presently employed within large vehicle climate control systems. By taking advantage of advances in the art of HVAC module design, such as brushless motor architecture, low pressure drop heat exchanger components, and refined scroll fan design, a single front module is able to provide the total required airflow for air conditioning of a large SUV or mini-van. The depicted HVAC module embodying of the present invention can provide 520 cubic feet per minute (CFM) airflow at 13 volts (VDC) in outside-air (OSA).

Referring to FIGS. 1 and 2, an HVAC module 10 includes an upper mode case 12 and a lower mode case 14. The HVAC module 10 has a housing assembly 16, an evaporator 18 and a heater core 20. The housing assembly 16 defines a primary inlet 24 for selective intake of outside air, a secondary inlet 26 for selective intake of recirculated cabin air, a first zone outlet 28 for conveying defrost air, a second zone outlet 30 for conveying upper cabin air to a driver and/or front cabin occupant, a third zone outlet 32 for conveying mid-level and/or lower cabin air to the left front cabin occupant (driver), a forth zone outlet 34 for conveying mid-level and/or lower cabin air to the right front cabin occupant, and a fifth zone outlet 36 for conveying left and/or right side rear cabin air to rear seat occupants. As illustrated in phantom in FIG. 2, a longitudinally extending duct 38 communicates the fifth zone outlet 36 into the rear passenger compartment (not illustrated).

The upper mode case 12 forms a first mixing chamber 42, the first zone outlet 28, which is selectively restricted or closed by a first mode valve 41 (illustrated as fully closed), the second zone outlet 30, which is selectively restricted or closed by a second mode valve 39 (illustrated as fully open), the third zone outlet 32 (illustrated in FIG. 1) which is selectively restricted or closed by a third mode valve (not illustrated), and the forth zone outlet 34 which is selectively restricted or closed by a fourth mode valve 43 (illustrated as fully closed). A temperature valve/blend door 48 selectively controls a first cold air stream 27 flowing through a cold air path 44 and a hot air stream 35 flowing through a hot air path 46 conjoining at the temperature valve/blend door 48 and flowing into the mixing chamber 42.

The lower mode case 14 forms a second mixing chamber 45 and the fifth zone outlet 36, which is selectively restricted or closed by a fifth mode valve 52 (illustrated as partially open). A temperature valve/blend door 50 selectively controls a second cold air stream 29 and a second hot air stream 37 flowing into the second mixing chamber 45. A third cold air stream 31 flows through heater core 20, and is transformed into first and second heated air flows 35 and 37. An inlet air flow 25 passes through the evaporator 18 and is trifurcated into separate cold air streams 27, 29 and 31.

A fan assembly 38 disposed within the housing assembly 16 selectively drives air from the primary/secondary inlets 24, 26 to the first through fifth zone outlets 28, 30, 32, 34 and 36, respectively. The evaporator 18 is supported by the housing 16 and is disposed downstream of the primary inlet 24. The evaporator 18 cools the air entering from one of the inlets 24, 26. A cold bias outlet 40 is defined by the housing 16.

The heater core 20 is supported by the housing 16 and is disposed downstream of the evaporator 18. The heater core 20 heats the cool air being delivered from the evaporator 18. A hot bias outlet (not illustrated) is defined by the housing 16. The housing 16 defines a mixing chamber 42 and a cool air path 44. The cool air path 44 conveys the cool air stream 27 from the evaporator 18 to the mixing chamber 42. Additionally, the housing 16 defines a heated air path 46 parallel to the cool air path 44. The heated air path 46 conveys air from the heater core 20 to the mixing chambers 42 and 45. The mixing chamber 42 receives and mixes cool air from the evaporator 18 and the hot air from the heater core 20. A temperature valve 48 is disposed between the heated air path 46 and the cool air path 44 for apportioning the flow of cool air originating in the evaporator 18 between the cool air path 44 (for airflow into the mixing chamber 42) and the heated air path 46 (for airflow through the heater core 28) then into the mixing chamber 42. A rear zone temperature valve 50 is disposed downstream of the heater core 20 to apportion airflow in the lower mode case 14 from the cool air path 29 and heated air path 37 to the fifth zone outlet 36. A rear zone valve 52 serves to restrict and/or shut off all airflow in the lower mode case 14 through the fifth zone outlet 36 and duct 38 leading to the rear passenger compartment.

One of the key design features of the High Performance Module is that it offers common cold and hot air stream access to the individual zones. Downstream of the evaporator and heater, there is no partition wall for forming multi-zone air streams. The airflow from the evaporator and the heater is open to all zonal air streams. The zonal air streams take on their own flow and temperature characteristics starting from a mixing zone downstream of the heater and evaporator, whereby partition walls are used to separate the airflows into distinct zones.

The high performance module 10 employs applicant's “Flexzone” architecture. In this construction, the front zone airflows and the rear zone airflows are formed separately with the “Upper Mode Case” 12 and the “Lower Mode Case” 14 as depicted in FIG. 2. The upper case 12 is designed to provide the airflow streams to the front two zones in the passenger compartment and the lower case 14 is designed to provide air streams to the rear two zones in the vehicle, either in the form of left/right rear zones or second/third row rear zones. As described previously, both of these cases 12, 14 share common airflow access from the heater 20 and the evaporator 18.

The benefit of “Open Airflow Access,” henceforth referred to as “Open Architecture,” is that each zone has full access to the entire airflow through the evaporator 18 and also the entire hot airflow through the heater 20. It is thus possible to provide “Super HVAC Module” operation with the full power of the HVAC module 10. However, this also represents a shortcoming of the Flexzone architecture: that airflow control changes from any zone can alter the airflow and possible temperature characteristics of all the other zones, causing airflow and temperature controllability issues.

The present invention provides a control method to enable independent zonal control whereby passengers located in each zone of the passenger compartment can obtain and maintain the desired airflow regardless of the operations by passengers in the other zones. It essentially disentangles the coupling of discharge airflow between zones due to the module architecture.

Airflow Control System Based on Velocity Sensors

Referring to FIG. 3, one embodiment of the present invention includes a HVAC control system 54 for a vehicle with a High Performance Module capable of supplying conditioned airflow streams for a quad-zone passenger compartment. (The principles embodied are applicable to any multi-zone air conditioning system.) An embedded microcontroller 56 monitors the user inputs in terms of discharge temperature, discharge flow rate, and discharge mode from all four zones. In addition, it also monitors flow rate sensors 58 from each zone as a feedback. The outputs from the microcontroller 56 modulate the operating state of the blower 60, positions of the temperature mix doors 62, and the discharge mode valves 64.

It is to be noted that as part of the mode control, two requirements must be met by the mode valves 64: (1) it is expected that in response to a positional command from the microcontroller 56 (such as an index indicating defrost, defog, heater, bi-level, vent, etc.), the mode control valves 56 are capable of providing the required airflow ratios to the defrost, heater, and vent outlets; (2) that it must have the capability to change the total effective flow area while guaranteeing the flow ratio requirements as set forth in (1). When the effective flow area is changed from zero to a pre-determined maximum area, the flow resistance of the path is changed to facilitate overall airflow balance for the vehicle.

FIG. 4 illustrates the control algorithm flowchart for the system of FIG. 3. The algorithm of FIG. 4 is contained in an iteration loop executed with pre-determined frequency such as every 0.1, 0.5 or 1.0 second depending on the capability of the microcontroller and the control response requirements. Upon entering the subroutine at step 68, the control targets are read in from each of the Human Machine Interface (HMI) units, commonly known as faceplate for each control zone of the passenger compartment at step 70. For the control of the system defined in FIG. 3, the key inputs are the zonal blower setting requirements (or flow rate requirements) and the mode setting requirements. Due to the feedback provided by the flow rate sensors, the inputs for the discharge temperature are not essential for the effective balance of the airflows except that they are translated into mix door positions which are directly executed by the microcontroller.

The blower setting requirements are subsequently converted into flow rate requirements for the different zones at step 72. Some zones may have higher airflow requirements than others, while other zones may require the airflow to be entirely shut off. These different requirements are embodied by the converted airflow rate targets for the corresponding zones. An additional, total airflow target is generated by summation of the zonal airflow targets in preparation for the actual blower control at step 74.

Subsequently, the air flow rate sensors are read at step 76. These sensors provide live feedback of the airflow in each of the control zones. It is expected that the flow rate sensor can be based on any of the commonly used air velocity sensors, such as hot-wire anemometers or thermistors. Regardless, the signals from the sensors are converted into airflow rate.

The blower control is performed based on the total airflow requirements from the HMI and the actually delivered airflow rate by summation of the converted flow rate sensor readings at step 78. Adjustment to the blower control, such as the blower voltage for direct current (DC) motors and pulse width modulation (PWM) duty cycles for brushless motors, is made by using proportional-integral-derivative (PID) control or its simpler form Proportional Control at step 80. The PID control input is the error between the total airflow targets and the total airflow delivered. This adjustment is made upon each entrance into the control subroutine at step 82.

Subsequent to the blower control adjustment, the zonal airflow balance instructions are executed. In this part of the control, an individual zonal airflow control target from the HMI is compared with actual airflow rate converted from its airflow sensor at step 84 to form the input to the second tier PID control. The process variable controlled is the total effective flow area for the zone as formed jointly by the opening of the mode valves. The total effective flow area may also be modified by a dedicated choke valve in series with the mode valves depending on the HVAC module architecture.

In this two-step process described in steps 76 through 96, each time the subroutine is executed, the blower operating level is changed and the airflow is re-balanced among the four zones. If one zone has a blower setting change, subsequent execution of the subroutine will make adjustment to the process control variables to ensure the new target is met for the changed zone and maintain the airflow for the unchanged zones.

Airflow Control System Based on HVAC Module Math Model

Embodiment 1, as described above, depends on the airflow sensors to provide airflow feedback from each zone. In Embodiment 2 of the present invention, we use a mathematical model of the HVAC module to replace the airflow sensors and provide feedback to the control algorithm. As shown in FIGS. 5 and 6, the sensor hardware has been removed from the HVAC module 102 and an HVAC Module mathematic model is incorporated as part of the microcontroller program 104.

The microcontroller 104 monitors the user inputs in terms of discharge temperature, discharge flow rate, and discharge mode from all four zones. The embedded microcontroller 104 includes a HVAC process module 106 and a HVAC mathematic module 108. The HVAC mathematic module 108 includes an HVAC module airflow model 110 fed by a heater mathematic model 112, an evaporator mathematic model 114 and a blower mathematic model 116. The HVAC mathematic module 108 includes feeds 118 of the various zone flow rates to the HVAC process module 106 which, in turn, includes temperature door position, mode door position and blower voltage feeds 120 to the HVAC module airflow model 110.

It can be seen that the microcontroller 104 executes at least two functional blocks of programming, with the two blocks interacting and exchanging information with each other. The HVAC control process algorithm, essentially defined in FIG. 4 with major modification (FIG. 7), processes the HMI user inputs, forwards the information onto the HVAC Module Mathematic Model 110, receives the calculated HVAC airflow rates for each zone of the passenger compartment from the Math model, and takes control actions by commanding the HVAC blower and mode valve effective area with operating parameters.

The HVAC Module Mathematical Model 110, on the other hand, provides zonal airflow estimates at any given blower voltage (or PWM duty cycle), mode valve positions, and mix door (aka temperature door) positions. The essential elements of the HVAC model should include a heater model 112, an evaporator model 114, a blower model 116, and a HVAC module airflow model 110 comprehending the mix door positioning and mode door positioning. The output from the HVAC Module Mathematic Model 108 includes at least the airflow rates for each of the climate control zones. It can further be enabled to provide discharge temperatures for each discharge zone. The calculated quantities are sent back to the “HVAC Control Process” 106.

Referring to FIG. 7, an alternative control algorithm 122 containing steps 124-158 which are substantially similar to corresponding steps 68-100 of algorithm 66 illustrated in FIG. 4, with the exception of step 134. In step 134 of algorithm 122, zonal flow rate Qi is calculated using the HVAC math model, contrasted with step 76 of algorithm 66 wherein zone “i” velocity sensor is read and converted to flow rate Qi.

To those skilled in the art of automotive air conditioning systems, various methods of modeling the HVAC model may be realized.

In-Vehicle Adaptive Correction of HVAC Module Math Model

It is known that the performance of the HVAC module changes over the life of the vehicle due to accumulation of dust particles in the air filter and over other components in the path of airflow, such as the heat exchangers, blower blades, plastic airflow ducts, and the like, or due to blower motor performance degradation. The HVAC module mathematic model, on the other hand, is not aware of the physical changes that take place in the HVAC module. The predictive capability of the HVAC mathematic model deteriorates over time. A direct consequence is that the requested airflow from the passengers will not be realized.

The present invention provides for a method 160 for the correction of the HVAC module mathematic model by way of a dedicated velocity sensor in a selected location in the HVAC module 10. FIG. 8 shows by way of example a single air velocity sensor 162 installed before the evaporator 18 and after the blower 60. The installation location of the sensor can be easily modified by those skilled in the art to various other locations in the airflow path of a HVAC module and ducts. The number of velocity sensors may be one or more, with the latter installed in FIG. 3.

The velocity sensor 162 is read during the first ignition cycle (preferably during the quality check in the vehicle assembly plant) to establish a baseline airflow velocity when the vehicle is brand new. FIG. 9 illustrates that during the initial baseline access of the velocity sensor, the HVAC module is operated by an algorithm 164 in a selected mode, blower speed, and temperature door position. This initially selected operating condition will be used later in the field so that a consistent basis of comparison is maintained. The value from the velocity sensor is stored in a non-volatile portion of the controller as variable “V_newcar” to be used for future correction of the mathematic model. Algorithm 164 is initiated by entering the subroutine at step 166.

In an initial logic step 168, if the host car is new, a command for selected blower voltage at step 170, followed by a command for selected discharge mode at step 172 and a temperature door position at step 174. Next, the velocity sensor is read at step 176 and the value V_newcar is stored to non-volatile memory at step 178. Lastly, the subroutine 164 is terminated at exit step 180. If the host car is not new, the ignition counter value IgCounter++is incremented at step 182 to keep track of ignition cycles. Next, at logic step 184, if MOD (IgCounter, 100) is not equal to zero, the program is immediately terminated at exit step 180. If, however, MOD (IgCounter, 100) is equal to zero (this is the illustrative case for every hundred ignition cycles), the program progresses to step 186 wherein a selected blower voltage command is issued, followed by a command for selected discharge mode at step 188 and a command for temperature door position at step 190. Next, the velocity sensor is read at step 192 and value V_current is stored to non-volatile memory at step 194. Lastly, the subroutine 164 is terminated at exit step 180.

While operating in the field, a counter is used to keep track of the number of ignition cycles. Even though the velocity sensor can be read continuously, it is preferred only to do so on a periodic basis to minimize disruption to the HVAC system operation as well as the clock cycle resource of the microcontroller. In FIG. 9, the non-limiting number of ignition cycle of 100 is used to initiate the reading of the sensor in the field. Once the specified ignition cycle is reached, the sensor is read and stored in the non-volatile memory as variable “V_current”. Along with variable “V_newcar”, “V_current” is to be used for correction of the HVAC module predicted zonal flow rate.

As shown in FIG. 10, the variables “V_newcar” and “V_current” are read before the HVAC module mathematical model is run to estimate the module zonal flow rates Qi. Once the control head desired settings Ti, Mi and Qi are read into the micro controller, the HVAC mathematic model is run to estimate the airflow rate for each zone of the passenger compartment. The HVAC module mathematical model is believed to predict the flow rate for a brand-new module. The predicted flow rate is then scaled down with the ratio of “V_current/V_new” to arrive at flow rates that are more reflective of the actual airflow in the physical module.

Referring to FIG. 10, an algorithm 196 is initiated at a step 198 in which the subroutine is entered, followed by a step 200 of reading V_newcar and a step 201 of reading V_current. Next, at step 202, zone “I” control inputs Ti, Mi and Bi are read and employed to calculate zonal flow rates Qi using the HVAC math model. Subsequently, at step 206, zonal flow rate is calculated as Qi,corr=Qi Vcurrent/Vnewcar. Lastly, algorithm 196 is terminated at exit step 208.

Super-Mode Control

As indicated earlier, the High Performance Module employs applicant's “Flexzone” architecture. Each zone of airflow delivery has “Open Airflow Access” to the hot stream going through an “enlarged” heater and an “enlarged” evaporator. The benefit of “Open Airflow Access” is that each zone has full access to the entire airflow through the evaporator and also the entire hot airflow through the heater. It is thus possible to provide “Super HVAC Module Operation Modes” with full power to the HVAC module.

The second enabler is the relatively large heater and evaporator in the High Performance Module. The design specification for the High Performance Module requires that the evaporator and the heater are large enough in heat transfer capacity to provide heating or cooling comfort for a large SUV or Mini-Van with multiple comfort zones. For the Mini-Van, the multi-zones may include the front left, front right, row 2 seats and row 3 seats comfort zones. For a SUV, the multi-zones may include front left, front right, rear left and rear right. Both of these systems may be considered quad-zone systems.

The “Open Airflow Access” and the large evaporator together allow the “Super Modes” to be defined for the front zone of the vehicle. Under certain vehicle conditions, such as windshield defrost, windshield defog, transient heating or transient cooling after ignition, the applicant proposes “Super Defrost”, “Super Vent”, and “Super Heater” operating modes to enhance HVAC performance.

The “Super Modes” of operation are realized by first shutting off all the rear climate control zones in the vehicle, and by operating the refrigeration and/or heating system at its maximum capacity. This eliminates the amount of heating or cooling consumed by the rear and makes them available to the front passengers. In the high blower settings, since the High Performance Module is designed to provide comfort for the entire vehicle, this “focused” application of heating or cooling to the front passengers enables the “super” performance for the front zone of the vehicle. It is to be recognized that for the majority of the time there are only front passengers in the vehicle. Thus, the “Super Vent” and “Super Heater” modes of operation should frequently and significantly enhance the front passenger comfort, especially during soak and cool-down or soak and warm-up. Meanwhile, the “Super Defrost” mode of operation should tremendously improve the performance of defrosting and defogging, allowing the vehicle to produce improved passenger safety.

Table 1 illustrates the exemplary standard definition of airflow distribution for a quad-zone climate control system. In the normal modes of operation, even if the rear zones are shut off, the maximum airflow allocation to the front zone will not to exceed the amount as allocated in the table. The “normal” modes design conforms to the present day accepted climate control design specification.

TABLE 1 Airflow Definition for “Normal Mode” Operation Airflow Distribution (CFM) “Normal” Lft/Rgt Operating Defrost Lft/Rgt Vent Mode Outlet Lft/Rgt Htr Outlet Outlet Lft/Rgt Total Defrost 240 30 0 270 Heater 30 240 0 270 Vent 0 0 300 300

Table 2 illustrates the exemplary “Super Mode” airflow definition. Due to the extra availability of heating or cooling from the enlarged heater and evaporator for the quad-zone system, there is sufficient HVAC conditioning power to process an increased amount of airflow without compromising the discharge temperatures. Therefore, for each of the “Super Mode” modes of operation, the airflow is increased by approximately 25-30%. With the increased airflow allocation, reduced time to comfort is achieved in the “Super Vent” and “Super Heater” modes, and faster defrost or defog performance is achieved to improve passenger safety.

TABLE 2 Airflow Definition for “Super Mode” Operation Airflow Distribution (CFM) “Super” Lft/Rgt Operating Defrost Lft/Rgt Vent Mode Outlet Lft/Rgt Htr Outlet Outlet Lft/Rgt Total Max Defrost 300 45 0 345 Max Heater 45 300 0 345 Max Vent 0 0 400 400

It is to be noted that the “Super Mode” airflows are not necessarily the maximum airflow that the High Performance Module can deliver at full vehicle power-bus voltage (e.g. 13 VDC). The amount of airflow for a “Super Mode” is carefully selected to optimize the overall passenger thermal comfort experience in the vehicle. The optimization criteria include impact air velocity at the surface of the front passengers, the noise increase associated with the increase of the airflow, dry-eye reduction in the “Super Defrost Mode”, etc.

FIG. 11 illustrates the control steps to be taken to achieve “Super Mode” operation. The first step is to read the control head input and identify if “Super Mode” operation is requested. If so, the rear zones are turned off by shutting off any shut-off valves in the airflow paths to the rear climate control zones. Meanwhile, the compressor is operated at the highest level possible without freezing the evaporator. For example, the electronic variable displacement control for the compressor is set to operate at full stroke. For winter operations, such as the “Super Heater” or “Super Defrost” modes, the PTC heater, if equipped, is powered to the full capacity. Finally, the HVAC blower is set to operation at the appropriate voltage level to provide the specified airflow rate defined for a particular “Super Mode”.

FIG. 11 illustrates a control algorithm 210 for achieving Super Mode operation of HVAC module 10. The control algorithm 210 is initiated by entering the subroutine at step 212, followed by the step of reading HVAC mode input at step 214. Following is a logic step 216 wherein if a Super Mode is selected, all rear zones are turned off at step 218. Next, the compressor (or PTC header) is operated at maximum power at step 220. Then, the blower is commanded to operate at Super Mode settings in accordance with a table in memory at step 222. Lastly, the subroutine is exited at step 224. If a Super Mode is not selected at step 216, normal HVAC system operation is executed at step 226 and the subroutine terminated at exit step 224.

Normal Mode

FIGS. 12, 13, 14A, and 14B show a method of operation of the HVAC system of one of FIGS. 3, 5, and 8 in a normal mode, i.e. during normal operation of a vehicle after an initial set-up when no Super Mode is required. FIG. 14B continues at points A and B at the bottom of FIG. 14 A.

In general, the following airflow control flowcharts describe the algorithm to balance airflow when mix door positions are dictated by an external DTM control method.

In particular, FIG. 12 illustrates an example of a separate Discharge Temperature Maintenance control (DTM control) method. The algorithm described in FIG. 12 is merely an example of how a temperature demand by a vehicle occupant may be handled by the DTM control. For example, in step 301, initially all zonal mix doors may be set to an initial position that, by non-limiting example, may be a middle setting, dividing the mix door cross-section into 50% allocation to the cold air chamber and 50% to the hot air chamber, or may be previously calculated mix door positions. The DTM control reads the zonal temperature request T by a vehicle occupant or an Automatic Climate Control system and subsequently, in step 302, performs an actual discharge temperature measurement (DTM) downstream of the respective mix door using temperature sensors such as thermistor. In step 303, the deviation between the actual DTM and zonal temperature request T is determined. In step 304, the DTM control determines if the absolute deviation is smaller than a permissible tolerance error. Without limitation, the tolerance error may be included in the permissible range so that the sign “<” may be replaced with “≦” in FIG. 12. If the deviation is below the permissible threshold, which may, for example be 1 degree Fahrenheit or 1 degree Celsius, the DTM subroutine is terminated in step 305.

Conversely, if the deviation is not within a permissible range, the mix door position is adjusted for more closely reflecting the temperature request in step 306. Subsequently, the steps, starting at step 303, are repeated until a satisfactory convergence of the DTM and the zonal temperature request T is achieved.

For the HVAC airflow control in a vehicle with a DTM control, this separate adjustment routine of the mix doors limits the number of available adjustments controlled by the HVAC airflow control. For example, the HVAC system may be limited to adjusting the blower voltage and the positions of the output valves (represented in FIG. 3 as modal valves 64) to achieve and maintain zonal airflow as requested.

As shown in FIG. 13, in step 307, the blower is started with a blower voltage V_(b) ^(k) that is set to an initial blower voltage V_(b) ⁰ corresponding to a preset minimum blower voltage V_(b,min).

In a next step 308, the subroutine shown in FIGS. 14A and 14B is performed for adjusting the positions of zonal output valves as described in more detail below. Once the output valve positions have been set according to FIGS. 14A and 14B, the blower voltage V_(b) ^(k) will be adjusted for optimized performance and efficiency in a subsequent typical control loop with the counter k.

Each of the output valves has, in its fully open position, a certain minimum attainable flow resistance R_(Mi,min), that may be retrieved from a lookup map in step 309. In steps 310 and 311, the respective minimum resistance for each output valve is compared to the calculated, needed output valve resistance R_(Mi) ^(k) of step 410 in FIG. 14B.

Step 310 determines whether the minimum attainable resistance R_(Mi,min), is greater than the needed resistance beyond a small threshold ratio of a few percent representing an allowed deviation. The threshold ratio is a normalized resistance deviation, i.e., the deviation divided by the respective minimum attainable valve resistance R_(Mi,min). The threshold ratio for the allowed individual resistance deviations may be a calibratable number whose value is to be optimized during vehicle development in climatic chamber or on the road. The threshold ratio, however, preferably is kept below 5%, such as 2%.

If the requested output valve resistance R_(Mi) ^(k) of any of the output valves is smaller than the minimum attainable resistance R_(Mi,min) under the given pressure conditions by more than the threshold deviation, the requested zonal target flowrate Q_(i) ^(targ) associated with the respective output valve is not attainable with the current blower voltage V_(b) ^(k). Accordingly, the blower voltage V_(b) ^(k) needs to be raised as shown in step 312. The incremental steps taken to raise the blower voltage may be proportional to the deviation of the requested output valve resistance R_(Mi) ^(k) from the minimum attainable resistance R_(Mi,min).

If, on the other hand, the requested output valve resistance R_(Mi) ^(k) of any of the output valves is not smaller than the minimum attainable resistance R_(Mi,min) by more than the threshold deviation, step 311 inquires if the requested output valve resistance R_(Mi) ^(k) exceeds the minimum attainable resistance R_(Mi,min) by more than the threshold deviation. The threshold deviation may be identical to or different than the threshold deviation of step 310, and the same considerations apply to the chosen percentage of the deviation in step 311 as in step 310. If all the requested output valve resistance R_(Mi) ^(k) exceeds the minimum attainable resistance R_(Mi,min) by more than the threshold deviation, the blower is not running at its optimum efficiency because blower pressure is generated that is subsequently unnecessarily throttled down by the output valves.

Thus, the blower voltage V_(b) ^(k) can be reduced in step 313 to improve the blower energy efficiency. The incremental steps taken to lower the blower voltage V_(b) ^(k) may again be proportional to the smallest of all deviations from step 311 of the requested output valve resistance R_(Mi) ^(k) from the minimum attainable resistance R_(Mi,min). The proportionality factor β for lowering the blower voltage may be identical to the proportionality factor α for raising the blower voltage, but different factors may be used.

The method is repeated from step 308 until at least one zone has a requested output valve resistance R_(Mi) ^(k) that closely matches the minimum attainable resistance R_(Mi,min) of the respective output valve as defined in steps 310 and 311.

Once at least one of the requested output valve resistances R_(Mi) ^(k) deviates from the respective minimum attainable resistance R_(Mi,min) by less than the threshold ratios, the method is completed in step 314. The method starts anew at step 301 if any of the manually set zonal control inputs changes.

The flowchart of FIGS. 14A and 14B depicts the subroutine 308 to place the output valves in optimized position for a given blower voltage. Superscript k, representing the k-th iteration of step 308 and “k” has been omitted in FIGS. 14A and 14B for simplicity.

As shown in step 401 of FIG. 14A, according to the proposed control method, the HVAC system first reads the current blower voltage V, temperature request inputs T_(i), mode request M_(i) (in this case the mode request is the “normal” mode, and a blower request B_(i) representative of an airflow percentage of the maximum air flow possible for the i'th zone. In step 402, the individual blower requests B_(i) are converted into zonal flowrate requests Q_(i) ^(targ) based on the physical architecture of the HVAC unit and of the vehicle, in which the HVAC system is installed. The mode request M_(i) may have been established at an earlier time before entering into the given subroutine for the normal mode.

In step 403, the flowrate requests Q_(i) ^(targ) are then added up for determining a total blower request Q_(t) ^(targ) in step 403.

The subroutine 308 initially sets the positions for the output valves to the fully open positions in step 404. Further, in step 405, the HVAC control reads the individual zonal temperatures DTM_(i) dictated by the DTM control loop, the outlet temperatures of the evaporator T_(e), the outlet temperature of the heater T_(h), and the mix door positions POS_(mix,i), dictated by the DTM control loop.

It should be noted that steps 401, 404, and 405 may be performed in any order or simultaneously as their functions do not depend on any one of the other steps.

From the readings of step 405, zonal flow blends are calculated as zonal percentages of the zonal airstreams in step 406. For example, the zonal hot air percentage PC_(i) ^(hot) may be calculated from the difference between the zonal DTM temperature DTM_(i) and the evaporator temperature T_(e) divided by the difference between the heater temperature T_(h) and the evaporator temperature. Conversely, the zonal cold air percentage PC_(i) ^(cold) may form the remainder of the zonal airstream of 100% by subtracting the hot air percentage PC_(i) ^(hot) from 100%.

From the previously calculated zonal flowrate requests Q_(i) ^(targ) and the respective individual requested hot air percentage PC_(i) ^(hot), a total hot air demand is determined in step 407 by adding up all individual products of Q_(i) ^(targ) and PC_(i) ^(hot) to a total hot stream airflow Q_(hot) ^(targ).

In step 408, an evaporator pressure drop ΔP_(e) caused by the evaporator can be calculated based on the total blower request Q_(t) ^(targ) (here named Q_(t)) and known correlations stored in an evaporator map that may be a table or a virtual model executing mathematical equations representing characteristics of the evaporator. The evaporator map may, for example, take into consideration pressure conditions resulting from the known HVAC unit architecture and optionally current settings of mix door and output valve positions. Further, from the heater pressure drop ΔP_(h) may be determined in a similar manner as the evaporator pressure drop ΔP_(e). Because only air that has passed the evaporator may reach the heater, the heater pressure depends on the evaporator pressure, on the requested total hot stream airflow Q_(hot) ^(targ) (here named Q_(t) ^(h)), and known correlations stored in a heater map that may likewise be a table or a virtual model executing mathematical equations representing characteristics of the heater. The heater map may, for example, take into consideration pressure conditions resulting from varying output valve positions.

Continuing in FIG. 14B, the subroutine 308 continues at step 409 by determining the pressure P_(b) generated by the blower from a stored blower map that may be a table or a virtual model executing mathematical equations representing characteristics of the blower. The blower map takes as inputs the blower voltage and the total airflow rate Qt through the blower to determine a blower-outlet pressure rise from its inlet pressure. The pressure at the outlet of the blower P_(b) ^(k) can be calculated using the inlet pressure and the pressure rise across the blower. The evaporator pressure drop ΔP_(e) ^(k) may be subtracted from the blower pressure P_(b) ^(k) to obtain an evaporator pressure P_(e) ^(k). Subsequently, the heater pressure drop ΔP_(h) ^(k) may be calculated and subsequently subtracted from the evaporator pressure P_(e) ^(k) to obtain the heater pressure P_(h) ^(k).

In step 410, Knowing evaporator pressure P_(e) ^(k), heater pressure P_(h) ^(k), and mix door positions POS_(mix,i) dictated by the DTM control loop, the hot airflow resistance R_(mix,i) ^(h) and cold airflow resistance R_(mix,i) ^(c) of each mix door can be determined from a mix door resistance map. The individual airflow resistance values R_(mix,i) ^(h) and R_(mix,i) ^(c) are then converted into pressure drops caused by the mixing valves according to the following equations

ΔP _(mix,i) ^(h) =R _(mix,i) ^(h)·(Q _(i) ·PC _(i) ^(h))² and

ΔP _(mix,i) ^(c) =R _(mix,i) ^(c)·(Q _(i) ·PC _(i) ^(c))²

In step 411, the individual pressure drops for each zonal mix door are converted to mix door pressures in each mixing space after the respective mix door. The cold air mixing pressure P_(mix,i) ^(c) is determined by subtracting the cold air mixing pressure drop ΔP_(mix,i) ^(c) from the evaporator pressure p_(e), while the hot air mixing pressure P_(mix,i) ^(h) is determined by subtracting the hot air mixing pressure drop ΔP_(mix,i) ^(h) from the heater pressure P_(h).

For setting the positions of the output valves, such differentiated information may not be required. Instead of utilizing the individual hot and cold pressures for each zone, the HVAC system generates an average zonal mixing pressure P_(mix,i) ^(avg) for each of the mixing valves. For example, it may use the arithmetic mean as shown in step 411. Thus, the system calculates what the pressure after each mix door would be if the airflow were at the requested flow rate. The calculation is done for the hot path and the cold path at the same time.

In step 412, knowing the mix door pressures P_(mix,i) ^(avg) for each zone, the system can calculate the resistance R_(Mi) of each zonal output valve that is needed to attain the desired zonal airflow Q_(i) by solving the equation

R _(Mi) =P _(mix,i) ^(avg) /Q _(i) ²

The zonal output valve resistances R_(Mi) are then entered into an output valve lookup map in step 413 to obtain the output valve positions POS_(mode,i) that correspond to the respective resistance values R_(Mi). In step 414, the individual zonal output valves are then placed to the retrieved positions POS_(mode,i) using actuators.

The average pressure for the combined hot and cold path is thus used to calculate an updated position for the output valves. In step 415, the difference between the two pressures P_(mix,i) ^(h) and P_(mix,i) ^(c) for each mixing valve is used as the criterion for convergence. The pressure difference is normalized by dividing it by the average zonal mixing pressure P_(mix,i) ^(avg) for each of the mixing valves. This normalized difference should be smaller than a threshold ratio, for example 2%. The threshold ratio may vary based on the location of the zone, based on the selected temperature, and/or based on the selected airflow as will be explained below. If the normalized pressure lies between −2% and +2%, for example, the output valve position has been adjusted and considered converged, and the subroutine of FIGS. 14A and 14B is exited in step 416 to return to the subroutine of FIG. 13 after completion of step 308. If the normalized pressure difference lies outside the threshold limits, steps 405 through 415 are reiterated with the current output valve positions POS_(mode,i) replacing the initial fully open positions of step 404.

During each iteration through step 405, both the mix door and output valve positions will be updated. The mix doors are extrinsically adjusted by the DTM controller, and the output valves are intrinsically adjusted by step 414. The calculation loop continues to iterate until convergence.

The lookup map for the blower uses voltage and airflow rate as inputs to look up the pressure head after the blower. The lookup maps for the heat exchangers (evaporator and heater) and the mix door or output valves are populated with pre-quantified airflow resistance values. The heat exchanger map is a function of airflow rate, and the valve map is a function of valve position. After looking up the resistance value R, the pressure drop is calculated as ΔP=R×Q². A valve map is also used in the reverse lookup of step to determine the valve position corresponding to a pre-determined resistance R=ΔP/Q². Below is an example for a valve map with 11 breakpoints:

Valve Position Pos(0) Pos(1) Pos(2) Pos(3) Pos(4) Pos(5) Pos(6) Pos(7) Pos(8) Pos(9) Pos(10) Valve R(0) R(1) R(2) R(3) R(4) R(5) R(6) R(7) R(8) R(9) R(10) Resistance

For example, with a pre-characterized blower map, a pre-defined airflow-resistance map for heat exchangers, and a resistance-position map for control valves, the pressure values upstream and downstream of each key system component can be calculated. Therefore, at a given voltage, the corresponding valve positions for the needed valve resistances can be calculated for delivering a requested airflow to each zone. The control method iterates the blower operating voltage from an initial value until at least one of the airflow control valves reaches its 100% open position within a tolerance range of, e.g., 2%. This number may be variable based on the total airflow. For example, a change of 2% can be felt at very high airflows but not at lower airflows where 2% may be a very tiny absolute number. Then the control method operates the blower at that specific voltage, which is the lowest possible to supply all the requested air flow, thus optimizing the energy utilization of the system.

In this context, pre-characterized maps have the advantage of obviating the need for additional pressure sensors in the flow path. The pre-characterized maps, which may be look-up tables or functional models describing correlations, can be established by standard empirical testing of sample HVAC systems prior to installation of the HVAC system. They reduce the need for additional real-time calculations. It has been found that this set-up adjusts valve positions and blower power within a short time in the order of 2-3 seconds.

In summary, the present application describes how various zone outputs with different airflow and temperature settings can be individually achieved with a single-blower HVAC unit while still attaining high energy efficiency at all times. In particular the presented control method is suited even for systems, in which the mix door positions are controlled externally by a DTM control system and are not accessible to the HVAC control. The blower voltage is optimized to be the minimal level necessary so that the system is operated in the most efficient way in terms of energy consumption by completely opening at least one of the output valves at any of the zone outlets, while achieving and maintaining delivered airflow and temperature for each individual zone outlet.

It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art. 

What is claimed is:
 1. A method of controlling the discharge of temperature-conditioned air from a plurality of zone outlets of an automotive HVAC system via an open architecture multi-zone HVAC unit having a single blower fan, an evaporator downstream of the blower and a heater downstream of the evaporator, wherein each zone in the module includes a temperature mix door for proportioning hot and cold air, which is controlled by a separate Discharge Temperature Maintenance control (DTM control), and an output valve for controlling a zonal output flow rate, the method comprising the steps of: reading a blower level request for each of the zone outlets; converting each zonal blower level request to a zonal flowrate request; calculating a total output flowrate request as a summation of all zonal flowrate requests; reading a mix door position that has been set by the DTM control for each of the zone outlets; reading a DTM sensor temperature for each of the zone outlets; determining a pressure downstream each mix door but before the output valve for each zone. determining, for each zone outlet, a target resistance for each output valve based on the zonal flowrate request and on the pressure downstream of the mix door; placing the output valve of each zone outlet in an output valve position associated with the target resistance; and operating the single blower fan at a minimum voltage required for generating the total output flowrate request.
 2. The method of claim 1, further comprising the steps of: setting an initial blower operating voltage; determining a minimum resistance for each of the output valves using pre-calibrated flow resistance table as a function of an outlet valve position; determining for each of the output valves a respective individual normalized resistance deviation of the calculated individual output valve resistance from the individual minimum attainable output valve resistance; placing each output valve in an adjusted output valve position associated with the respective individual normalized resistance deviation; and modifying the blower voltage to operate the single blower fan at a minimum voltage required for generating the total output flowrate request with the outlet valve position of at least one of the output valves set to the minimum attainable output valve resistance.
 3. The method of claim 2, further comprising the step of determining the adjusted output valve position for each zone based on an average mixing pressure downstream of each mix door.
 4. The method of claim 3, further comprising the steps of calculating the average zonal mixing pressure for each zone in a mixing chamber between each one of the mix doors and an associated output valve, the average mixing pressure being the arithmetic mean of the hot air pressure and the cold air pressure downstream of each mix door, and determining a desired output valve resistance from the average mixing chamber pressure.
 5. The method of claim 2, further comprising the steps of: determining an individual normalized resistance deviation of the calculated individual output valve resistance from the individual minimum attainable output valve resistance for each of the output valves; wherein the step of adjusting the blower voltage brings at least one of the individual normalized resistance deviations below a predetermined threshold ratio such that at least one of the outlet valves is fully open.
 6. The method of claim 2, wherein a minimum attainable resistance of each output valve is based on predetermined stored output valve calibration data.
 7. The method of claim 5, wherein the threshold ratio for the individual normalized resistance deviations amounts to at most 5 percent.
 8. The method of claim 1, wherein each output valve is initially set to a fully open position with minimal flow resistance until each output valve in an output valve position associated with the respective individual normalized resistance deviation sets a different output valve position.
 9. The method of claim 1, wherein the blower voltage is initially set to a minimum operating voltage until the blower voltage is adjusted.
 10. The method of claim 1, further comprising the step of: converting for each zone a DTM sensor measured temperature to a zonal hot air flowrate percentage of the zonal flowrate request.
 11. The method of claim 10, further comprising the step of reading an evaporator outlet temperature and a heater outlet temperature for determining the hot air flowrate percentages.
 12. The method of claim 11, further comprising the step of calculating a total hot air flow rate request from all zonal hot air flowrates.
 13. The method of claim 1, further comprising the steps of: calculating an evaporator pressure downstream of the evaporator; calculating a heater pressure downstream of the heater; wherein the step of adjusting the blower voltage takes pressure drop associated with each mix door position into consideration.
 14. The method of claim 13, wherein the evaporator pressure is determined from a total air flow and an evaporator pressure drop, which is determined from predetermined stored evaporator calibration data.
 15. The method of claim 13, wherein the heater pressure is determined from a total hot air flow rate and a heater pressure drop, which is determined from predetermined stored heater calibration data.
 16. The method of claim 1, wherein each output valve position is determined by using the calculated required resistance through a calibrated look-up table for the output valves.
 17. The method of claim 1, wherein the pressure drop of each of the temperature mix doors is determined by at least the following steps: looking up a hot air resistance value associated with the mix door position determining a hot air pressure drop from the hot air resistance value, the zonal flow rate request, and from a zonal hot air flowrate percentage of the zonal flowrate request; looking up a cold air resistance value associated with the mix door position; determining a cold air pressure drop from the cold air resistance value, the zonal flow rate request, and from a zonal cold air flowrate percentage of the zonal flowrate request.
 18. The method of claim 1, wherein the output valves comprise a plurality of parallel mode valves.
 19. The method of claim 1, wherein the output valves comprise at least one dedicated flow control valve. 